Existing hydraulic tools, such as hydraulic wrenches, generate heat as result of the use of high temperature hydraulic fluid passing through the tool. The user grips a grip which surrounds a metal valve body through which the high temperature hydraulic fluid passes. It is desirable to prevent the transfer of this heat to the user's hand. The prior art insulates the metal valve body with a PVC-based dip, which tends to be inadequate to prevent the passage of heat generated by the high temperature hydraulic fluid. In addition, the PVC-based dip is not very durable and is not easy to replace if the tool becomes damaged.
Such press units are known in various embodiments. Reference is made to WO 99/19947, for example, as well as WO 98/24570, relating to use as a punching device, WO 02/62504, relating to use as a sizing tool, and WO 02/00368, relating to use as a riveting device.
A press unit of this kind is also known from DE 20 2004 000 215 U1, for example. As a result of a design of the control valve as a check valve, the hydraulic medium which is delivered by the pump passes through the control valve from the inflow side to the outflow side, the control valve being situated in a hydraulic line leading from the hydraulic-medium pump to the hydraulic cylinder which accommodates the hydraulic piston. When the hydraulic-medium pump is switched off, the hydraulic-medium pressure which is present on the outflow side together with a biasing spring which acts in the same direction causes the control valve to move into the open position, thus opening the hydraulic-medium outlet associated with the outflow side. Since in addition the control valve does not open at a higher system pressure, the control valve still does not open at the start of the return flow of hydraulic medium, when the return valve has opened after completion of a pressing operation.